That seems to be a fairly common conversion "back in the day". Several of mine have it also. I would guess someone like Doug Turnball could weld it up and then refinish the gun to make it original, but that would mean a refinish and a lot of expense.
I would suggest you consider enjoying it as is, but if you really want an original looking one, trade yours off to one of the 38/44 collectors (like me or others) and get what you really want.
Welding up and refinishing a nice pre-20 is a sad thing to a collector like me.